Commercial windows and door frames typically provide for the attachment of weatherstripping around closure surfaces to reduce the amount of cool air and moisture that can seep around the door or window. Although weatherstripping may be attached in many ways, a typical way as shown in FIG. 1 is to provide a T-slot “T” at an appropriate location around the periphery of the door or window. Referring to FIGS. 2 and 3, weatherstripping adapted for installation in T-slot typically has a base portion or backing “B” and a sealing portion “S”, which is often made of a yarn pile “P” and may include a barrier fin “F” of the type described in U.S. Pat. Nos. 3,175,256 and 4,148,953 to Horton. The base, sealing and fin portions are typically made of a thermoplastic polymer such as polypropylene. Backing B is a woven, and typically polymer coated, backing which retains the weatherstripping in the T-slot and minimizes the amount of dimensional stretch and/or shrinkage that the weatherstripping experiences as a result of stresses induced in its polymeric composition by installation and/or thermal effects of its manufacture. It is well known that thermoplastic weatherstripping, such as that made out of polypropylene, is prone to stretching and shrinkage caused by residual and induced stresses incurred during manufacture and installation. Also, the woven backing, which consists essentially of interlocking loops of polymer threads as described in U.S. Pat. No. 3,175,256 to Horton, stretches because the loops tend to straighten somewhat under a tensile load, causing an overall increase in backing length.
In most cases, installation of the weatherstripping entails inserting backing B into the T-slot of the frame member at one end and pulling it through the T-slot along its entire length until the weatherstripping is fully inserted in the T-slot. In one method of manufacture, the ends of the weatherstripping are then trimmed to the length of the window or door profile. The profile may be used immediately to construct a door or window, or may be stored with weatherstripping installed therein for later use.
Additional weatherstripping stretch is typically induced during installation. Frictional forces in the slot and variations in the slot profile along its length create a drag force on the weatherstripping as it is pulled into the T-slot. Depending on the size and shape of the profile and on the type of weatherstripping used, this drag force can be 0.5 pounds per foot of length of weatherstripping, or more. Where polypropylene weatherstripping is used, this drag force can stretch the weatherstripping more than 0.5 inches for every 10 feet of window or door profile. The amount of stretch can be increased further by the presence of an undersized slot, variations in the slot along its length, contaminants in the slot, variations in the backing thickness or width, curves or twists in the weatherstripping profile, rough surfaces on either the slot or the weatherstripping and a very long continuous profile length.
Weatherstripping shrinkage occurs due to the recovery from tensile stresses induced in the backing during the manufacture of the weatherstrip and/or its installation into the T-slot. Shrinkage is particularly worrisome because the weatherstripping is provided to create a continuous barrier around the perimeter of the window. However, any shrinkage that occurs after the weatherstrip is cut to size in the T-slot will create gaps in the weather barrier around the perimeter of the door or window. Thus, if the weatherstripping is cut prior to recovery from this stretch, portions of the window or door may be unsealed.
Numerous solutions to the problem of weatherstripping thermoplastic stretch and shrinkage have been proposed. One method, for use with extruded vinyl windows, is to insert the weatherstripping into the vinyl window length during the extrusion of the vinyl profile, thereby eliminating the pull force which causes stretching. In a related solution, U.S. Pat. No. 4,458,450 to Young et al. discloses a pile weatherstrip with a hinged backing to permit the weatherstripping to be inserted into the T-slot directly, rather than pulled through the length of the profile. Another solution disclosed in U.S. Pat. No. 5,384,976 to Hall, is to fuse the pile fibres together in the vicinity of the backing to reduce their width and thereby allow them to slide more easily through the T-slot. U.S. Pat. No. 4,860,495 to Kessler discloses a lower friction pile weatherstrip to reduce the drag force experienced when it is pulled it into the T-slot. Another common practice, discussed in U.S. Pat. No. 5,979,036 to Socci et al., is to tack or stake the weatherstripping to the profile periodically along its length to minimize the unfixed lengths of weatherstripping in the profile, thereby reducing the amount by which the weatherstripping is permitted to shrink.
Prior art solutions remain unsatisfactory, however, mainly because of their overall ineffectiveness and/or associated expense. Accordingly, there is a need for thermoplastic weatherstripping with improved anti-stretch and anti-shrink characteristics.